A direct injection diesel engine is an internal combustion engine in which injected fuel is ignited as a result of temperature and pressure conditions within a combustion chamber. The characteristics of the pistons forming the combustion chamber in the engine are particularly important with respect to efficiency and engine-out emissions. For example, engines are subject to increasingly stringent emissions standards for particulate matter, a source of which may be soot formation in the combustion chamber. Accordingly, there is a need for pistons that minimize soot formation.